Fiber connecting method, laser apparatus and projection television

ABSTRACT

A fiber connecting method and a laser apparatus using the fiber connecting method are disclosed. A plurality of fibers are bundled into a fiber bundle. The ends of the plurality of the fibers are connected to an end of a single-core fiber having a larger core diameter than the plurality of the fibers. The plurality of the fibers have different directions and characteristics depending on the position connected to the single-core fiber.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2002-189945, filed Jun.28, 2002, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a fiber connecting method forcombining a plurality of laser beams by bundling a plurality of fibersand connecting them to a single-core fiber, and a laser apparatus and aprojection television using the method.

[0004] 2. Description of the Related Art

[0005] The conventional method of connection employed in the field of apumping semiconductor laser of a solid laser using an optical fiberbundle will be explained. In Jpn. Pat. Appln. KOKAI Publication No.2001-15839, an “optical fiber pumping solid laser apparatus” isdisclosed, in which a laser beam generator having a high pumpingefficiency is obtained by connecting an optical fiber bundle with aplurality of fiber output semiconductor lasers and a single-core opticalfiber to each other. The advantages described in this publication arethat a high connecting efficiency can be achieved by combining the sizeof the outer periphery of the core of the fiber bundle and the corediameter of the single-core fiber and that the use of a single-core cansuppress the irregularities of the laser beams emitted from the cores ofthe fiber bundle.

[0006] This prior art is based on a prerequisite that the laser beamsfrom the fiber bundle have the same characteristics, and thereforeintended to mix a plurality of laser beams to some degree and therebyobtaining a uniform output as a whole.

[0007] When the laser beams from the fiber bundle have differentcharacteristics or, for example, have different wavelengths, however,the laser beams from the fibers are required to mix with each otheruniformly.

[0008] Normally, a laser beam is propagated through a fiber in any ofpredetermined several mode patterns unique to each fiber. The laser beamentering a fiber propagates through the fiber by being connected with amode pattern capable of propagation. Frequently, however, the laser beampropagates in a mode pattern first connected. Therefore, the differenceof the incidence point is directly reflected in the difference of theconnecting mode pattern. This poses the problem that the exit patternfrom the single-core fiber is varied from one wavelength to anotherdepending on the point of incidence. The problem is especially seriousin an application of a display for obtaining white light.

[0009] Specifically, when a fiber bundle and a single-core fiber areconnected with each other, the exit pattern from the single-core fiberis varied with the position of each fiber in the fiber bundle. Thusirregularities are caused, thereby posing the problem that it isimpossible to obtain an exit light having a uniform mixture of laserbeams.

BRIEF SUMMARY OF THE INVENTION

[0010] According to an aspect of the invention, there is provided amethod of connecting fibers, comprises combining a plurality of fibersinto a fiber bundle; and connecting each one end of the plurality offibers to an end of a single-core fiber having a larger core diameterthan the fibers, the fibers having different directions andcharacteristics at different positions connected with the single-corefiber.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0011]FIG. 1 is a sectional view showing inclined fibers bundled and asingle-core fiber according to a first embodiment of the invention.

[0012]FIG. 2 is a sectional view showing fiber bundled and having aninclined cut surface and a single-core fiber according to an embodimentof the invention.

[0013]FIG. 3 is a block diagram showing a laser apparatus using a fiberconnecting method according to an embodiment of the invention.

[0014]FIG. 4 is a sectional view showing an example of fibers bundledaccording to an embodiment of the invention.

[0015]FIG. 5 is a sectional view showing an example of fibers bundledaccording to an embodiment of the invention.

[0016]FIG. 6 is a diagram for explaining the operation of a fiberaccording to a second embodiment of the invention.

[0017]FIG. 7 is a sectional view showing an example of fibers accordingto the second embodiment of the invention.

[0018]FIG. 8 is a block diagram showing an example of a projectiontelevision using a laser apparatus according an embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0019] A fiber connecting method and a laser apparatus using the fiberconnecting method according to an embodiment of the invention will beexplained in detail below with reference the accompanying drawings.

[0020] [First Embodiment]

[0021] According to a first embodiment, there are provided a fiberconnecting method in which a plurality of fibers forming a fiber bundlehave different directions depending on the position connected to asingle-core fiber, and a laser apparatus using the same method. FIG. 1is a sectional view showing a fiber bundle having inclined fibers and asingle-core fiber according to a first embodiment of the invention, FIG.2 a sectional view showing a fiber bundle having fibers with inclinedcut surfaces and a single-core fiber according to a first embodiment ofthe invention, FIG. 3 is a block diagram showing a laser apparatus usingthe fiber connecting method, FIG. 4 is a sectional view showing anexample of fibers bundled, and FIG. 5 is a sectional view showing anexample of fibers bundled.

[0022] With reference to these drawings, a laser apparatus using thefiber connecting method according to an embodiment of the invention willbe explained. As shown in FIG. 3, a laser beam from a laser generatorA21 enters an optical fiber 41 through a light coupler 31. Similarly,the laser beams from laser generators B22 to G27 enter optical fibers 42to 47 through light couplers 32 to 37, respectively. The seven fibers 41to 37 are bundled as a fiber bundle 51 and connected to a single-corefiber 11, as shown in FIG. 4.

[0023] The laser beams from the laser generators 21 to 27 have not thesame wavelength but generate two or more different wavelengths. In theprocess, the optical fiber 44 entered by the laser beam from the lasergenerator D is arranged at the central position D while the other fibers41 to 43, 45 to 47 are arranged at the outer peripheral portions A to C,E to G, respectively, in FIG. 4. When these optical fibers woulddirectly enter the single-core fiber 11 without being subjected to anyprocessing, the laser beams having different wavelengths would notsufficiently be mixed and constitute an irregular exit light.

[0024] Consequently, with a fiber connecting method according to anembodiment of the invention, as shown in FIG. 1 showing a part cut alongthe dashed line in FIG. 4, the fibers are bundled in such a manner thatthe optical axes of the exit beams of the optical fibers are directed tocross each other at a point, with the optical fibers arranged at theouter peripheral portion directed toward the center of the single-corefiber 11. As a result, the output beams from the fibers of the fiberbundle cross each other and are easily converted into a commonconnecting mode when entering the single-core fiber. Thus, the outputlaser beams from the laser generators A21 to G27 are easily mixed in thesingle-core fiber 11, so that the exit beams from the fibers 41 to 47become uniform as the laser beams from the laser generators aresufficiently mixed with each other.

[0025] The laser generators of the laser apparatus emit a red laserbeam, a green laser beam and a blue laser beam, each in monochromaticform, which are combined to obtain a white laser beam frequently. Thelaser generators A21 to G27 shown in FIG. 3 obtain monochromatic lasersof red, green and blue, respectively. Preferably, however, also when thethree fibers 52 to 54 carry red, green and blue lasers, respectively,the white laser light with the laser beams combined can be obtained asshown in FIG. 5.

[0026] By setting the cut surface of the connecting portion of eachfiber at an angle (for example, several degrees) as shown in FIG. 2, thesame operation and effects as if the direction of each fiber is changedcan be achieved. Specifically, as shown in FIG. 2, an inner fiber 16 hasa cut section perpendicular to the fiber direction, while outer fibers15, 17 have a cut surface not perpendicular but at an angle to the fiberdirection. For this reason, the laser beams are radiated toward thecenter axis of the single-core fiber 11 in accordance with each angle,thereby making it possible to obtain a uniform exit light beam with thelaser beams sufficiently mixed with each other.

[0027] As described above, according to the first embodiment of theinvention, a plurality of fibers forming a fiber bundle are arranged indifferent directions in accordance with the positions thereof connectedwith the single-core fiber. Thus, a fiber connecting method and a laserapparatus using the method are provided in which an exit light beam freeof irregularities can be obtained even when laser beams of differentwavelengths are radiated.

[0028] [Second Embodiment]

[0029] According to a second embodiment, there is provided a fiberconnecting method and a laser apparatus using the method, in which aplurality of fibers forming a fiber bundle have differentcharacteristics in accordance with the position of connecting with thesingle-core fiber. FIG. 6 is a diagram for explaining the operation of afiber according to a second embodiment of the invention, and FIG. 7 is asectional view showing an example of a fiber according to a secondembodiment of the invention.

[0030] In the second embodiment, unlike in the first embodiment, a fiberconnecting method is provided in which the fibers are not set at anangle but a uniform exit light beam can be obtained in accordance withthe characteristics of each fiber and each laser beam. Specifically, inFIG. 2, consider incident light beams and exit light beams 64, 65, 66 ofan optical fiber 44 assuming the center of the fibers. Assume that theincident light beams are such that the exit beams 65, 66 of high-ordermode represent a main portion of the exit light while the exit lightbeam 64 of low-order mode represents a small proportion. The low-ordermode is defined as a mode in which the incident light is radiated instraight and the high-order mode as a mode of the light diffused andreflected in different directions. In order to obtain an exit light beamof high-order mode, the light that has entered the light coupler 34shown in FIG. 3 is required to have an angle to the direction of theincident light beam. For obtaining an exit light beam of low-order mode,on the other hand, the light beams incident to the light couplers 31 to37 are required to have no angle.

[0031] As described above, as shown in FIG. 7, in accordance with thefiber position, the light beams enter the outer optical fibers 62, 63,etc. (corresponding to the fibers 41, 47 shown in FIG. 3) from the lightcouplers 31 to 37 without any angle of incidence to assure the low-ordermode. With the inner optical fiber 61 (corresponding to the fiber 44 inFIG. 3), on the other hand, the direction of the incident light beamsfrom the light coupler 34 are set at an angle to assure the high-ordermode.

[0032] As a result, the light coupler 34 is connected with the lasergenerator D24 to operate mainly in such a manner as to assure thehigh-order mode of the exit light beams from the optical fiber 44. Inthis case, as shown in FIG. 6, the laser beams 65, 66 enter thesingle-core fiber 11 in the directions at a larger angle of incidencethan the beam 64. The beams 65, 66 thus are more easily connected withthe high-order mode of the single-core fiber 11 and thus more easilymixed with the exit beams from the other fibers placed outside, therebyobtaining a uniform exit light beam.

[0033] An exit beam more easily connected with the high-order mode canbe alternatively obtained by increasing the numerical aperture (NA) ofthe inner optical fiber 44 as compared with that of the outside opticalfibers of the bundle, as shown in FIG. 7, as another method. Thenumerical aperture of a fiber is determined by the refractive indexes ofthe materials of a core and a cladding thereof, and it is preferable toemploy a fiber having a high NA of 0.35 and a low NA of 0.30, forexample.

[0034] The aforementioned two methods may be employed at the same time,or more effectively implemented with the features of the firstembodiment.

[0035] As described above, according to the second embodiment, a fiberbundle is composed of a plurality of optical fibers entered by laserbeams generated from a plurality of laser generators. When the fiberbundle is connected with a single-core fiber, the exit light beams fromthe single-core fiber can uniformly mix with each other without beingaffected by the position of each fiber forming the fiber bundle.

[0036] [Third Embodiment]

[0037] According to a third embodiment, there is provided a projectiontelevision having a laser apparatus embodying the present invention as alight source. FIG. 8 is a block diagram showing an example of aprojection television employing a laser apparatus according to anembodiment of the invention.

[0038] The projection television P according to the third embodimentshown in FIG. 8 comprises at least a light source 71 having a structureaccording to the first or second embodiment, a signal processing unit 73for processing an external video signal in a predetermined way andsupplying a control signal to an optical engine 72, the optical engine72 composed of a DMD or a liquid crystal irradiated with light from thelight source 71 for generating an image light in accordance with thecontrol signal, and a projection lens 74 for projecting the image lightfrom the optical engine 72 to a display 75.

[0039] A laser apparatus according to an embodiment of the invention isfor obtaining a uniform exit light beam and provides a high-qualityreproduced image, for example, when used with the light source, etc. ofthe projection television according to the third embodiment.

[0040] With the various embodiments described above, those skilled inthe art can realize the present invention. Nevertheless, it is easy forthose skilled in the art to conceive various modifications of theaforementioned embodiments, and the invention is easily applicable bythose skilled in the art to various embodiments without any inventiveability. The present invention, therefore, covers a wide range ofapplications without departing from the disclosed principle and thenovel features, and is not confined to the embodiments described above.

[0041] As explained above, with the fiber connecting method and thelaser apparatus using the same method according to an embodiment of theinvention, a uniformly mixed exit light beam can be obtained from asingle-core fiber without being affected by the position of each fiberforming a fiber bundle connected with a single-core fiber.

What is claimed is:
 1. A method of connecting fibers, comprising:combining a plurality of fibers into a fiber bundle; and connecting eachone end of said plurality of fibers to an end of a single-core fiberhaving a larger core diameter than the fibers, the fibers havingdifferent directions and characteristics at different positionsconnected with the single-core fiber.
 2. A method of connecting fibersaccording to claim 1, wherein each of said plurality of fibers formingthe fiber bundle is directed at an angle toward the center axis of thesingle-core fiber.
 3. A method of connecting fibers according to claim1, wherein each end of said plurality of fibers forming the fiberbundle, which end is connected to the single-core fiber, has a crosssection at an angle.
 4. A method of connecting fibers according to claim1, wherein said plurality of fibers forming the fiber bundle are threefibers for a red laser, a blue laser and a green laser, respectively. 5.A method of connecting fibers according to claim 1, wherein saidplurality of fibers forming the fiber bundle are entered by light beamsat different angles of incidence in such a manner that the exit lightbeam of the outer fibers of the bundle assumes a low-order mode and theexit light beam of the inner fiber of the bundle assumes a higher orderof mode than the outer fibers of the low-order mode.
 6. A method ofconnecting fibers according to claim 1, wherein said plurality of fibersforming the fiber bundle are such that the outer fibers of the bundlehave a low numerical aperture and the inner fiber of the bundle has ahigher numerical aperture than the outer fibers having a low numericalaperture.
 7. A laser apparatus comprising: a plurality of lasergenerators; and a group of fibers including a plurality of fibersconnected to each of the laser generators and a single-core fiberconnected to a fiber bundle including said plurality of fibers andhaving a larger core diameter than the fibers, wherein said plurality offibers have different directions and characteristics in accordance withthe position connected.
 8. A laser apparatus according to claim 7,wherein each of said plurality of fibers forming the fiber bundle isdirected at an angle toward the center axis of the single-core fiber. 9.A laser apparatus according to claim 7, wherein each of the ends of saidplurality of fibers forming the fiber bundle, which ends are connectedto the single-core fiber, has a cross section at an angle.
 10. A laserapparatus according to claim 7, wherein said plurality of fibers formingthe fiber bundle are three fibers irradiated with a red laser, a bluelaser and a green laser, respectively, by the laser generators.
 11. Alaser apparatus according to claim 7, wherein said plurality of fibersforming the fiber bundle are entered by light beams at different anglesof incidence so that the exit light beams from the outer fiber of thebundle have a low-order mode and the exit light beam from the innerfiber of the bundle has a higher order of mode than the outer fiberhaving a low order mode.
 12. A laser apparatus according to claim 7,wherein said plurality of fibers forming the fiber bundle are such thatthe outer fibers of the bundle have a low numerical aperture and theinner fiber of the bundle has a higher numerical aperture than the outerfibers having a low numerical aperture.
 13. A projection televisioncomprising: a light source including a plurality of laser generators, aplurality of fibers connected to each of the laser generators, and asingle-core fiber connected to a fiber bundle formed of said pluralityof fibers and having a larger core diameter than the fibers, saidplurality of fibers having different directions and differentcharacteristics in accordance with the position connected; and a displayfor displaying an image based on the video information supplied thereto,using the light radiated from the light source.
 14. A projectiontelevision according to claim 13, wherein each of said plurality offibers forming the fiber bundle is directed at an angle toward thecenter axis of the single-core fiber.
 15. A projection televisionaccording to claim 13, wherein each end of said plurality of fibersforming the fiber bundle, which end is connected to the single-corefiber, has a cross section at an angle.
 16. A projection televisionaccording to claim 13, wherein said plurality of fibers forming thefiber bundle are three fibers for a red laser, a blue laser and a greenlaser, respectively.
 17. A projection television according to claim 13,wherein said plurality of fibers forming the fiber bundle are entered bylight beams at different angles of incidence in such a manner that theexit light beam of the outer fibers of the bundle assumes a low-ordermode and the exit light beam of the inner fiber of the bundle assumes ahigher order of mode than the outer fibers of the low-order mode.
 18. Aprojection television according to claim 13, wherein said plurality offibers forming the fiber bundle are such that the outer fibers of thebundle have a low numerical aperture and the inner fiber of the bundlehas a higher numerical aperture than the outer fibers having a lownumerical aperture.